Stereo signal demonstrator



April 19, 1966 F. 1.. WAY 3,247,321

STEREO S IGNAL DEMONSTRATOR Filed Aug. 21, 1962 2 Sheets-Sheet 1 K 3/ 30 7/ I; I5 -22 Ifi N? g i 26 :26 i 1 20 /3 27/ 35 2/ W E@ RIGHT CHANNEL 26 28 26 y I 25 15 27 p 3? M Q T ANNE 28,29 26' LEF CH L /c I ?.26 j 52, 25

INVENTOR. FREDERICK L. WAY

his ATTORNEYS April 19, 1966 F. L. WAY 3,247,321

STEREO SIGNAL DEMONSTRATOR Filed Aug. 21, 1962 2 Sheets-Sheet 2 RIGHT CHANNEL LEFT CHANNEL INVENTOR. FREDERICK L. WAY

his ATTORNEYS United States Patent Ofiice 3,247,321 Patented Apr. 19, 1966 3,247,321 7 STEREO SIGNAL DEMONSTRATOR Frederick L. Way, Whitestone, N.Y., assignor to Mobilcolor, Inc., New York, N.Y. Filed Aug. 21, 1962, Ser. No. 218,285 10 Claims. (Cl. 1791) This invention relates to devices for demonstrating the separation of audio signals of different frequencies in a stereophonic system and, more particularly, to a new and improved signal demonstrator characterized by its simplicity and low cost of construction and operation.

In stereophonic sound reproducing systems, it is desirable to provide a visual display of the audio signal intensities at different frequencies in the two channels of the system, either to assist'in balancing the system initially or to emphasize for a listener the spatial separation of the source of sounds having different tonal characteristics.

Furthermore, even without stereo, the effect of an audio signal can be enhanced by presenting a visual display of the intensities of the various frequency components. Heretofore, however, electronic meters and the like have been used to provide visual representation of audio signals and these representations are usually purely informative and do not add to the esthetic effect of the stereophonically reproduced sounds.

Accordingly, it is an object of the present invention to provide a new and improved stereo signal demonstrator which overcomes the above-mentioned disadvantages of the present systems.

Another object of the invention is to provide a stereo signal demonstrator having a simple and inexpensive structure.

Still another object of the invention is to provide a device for representing visually, the intensities of the various frequency components of an audio signal.

A further object of the invention is to provide a stereo 'signal demonstrator which enhances the stereo effect produced by audio signals reproduced in a stereophonic system.

These and other objects of the invention are attained by providing a plurality of magnetic switch means each responsive to the magnitude of a. magnetic field so 'as to close and open in accordance with changes in the intensity of the field, a corresponding plurality of illuminating means connected to receive current through the magnetic switch means, and means adjacent to each magnetic switch means for generating a magnetic field in response to the amplitude a corresponding frequency component of an audio signal. Preferably, the various illuminating means produce different colors of light and, for stereophonic systems, the corresponding illuminating means in the two sets have the same colors.

Further objects and advantages of the invention will be apparent from a reading of the following description in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic electrical circuit diagram illustrating one form of stereo demonstrator according to the invention; and

FIG. 2 is a schematic electrical circuit diagram showing a further form of the invention.

In the representative embodiment of the invention shown in FIG. 1, two pairs of terminals 10, 11 and 10, 11 receive right and left stereo information signals and apply them to two loudspeakers 12 and 12', respectively, for representation of the various sounds in their originally spaced relationship and also apply them to two transformers 13 and 13' for transmission through the right and left channels, respectively, of the stereo signal demonstrator. Inasmuch as these two channels are identical in arrangement and operation, only the right channel .will be described in detail herein, the corresponding elements of the left channel being designated in the drawing by primed reference numerals.

From the coil 14 of the transformer 13, which has .a low input impedance, such as 8 ohms, corresponding to that of the loudspeaker 12 and a high output impedance, for example 500 ohms, the audio signal is applied through two conductors 1.5 and 16 to the energizing coil 17 of a magnetic reed switch 18. This switch comprises a glass envelope 19 axially disposed within the coil 17 which encloses a pair of normally spaced reed-type contact elements 20 and 21, at least one of which is made of magnetic material. To respond to signals applied to the coil .17, the contacts are disposed so that when the coil 17 is energizing sulficiently, they will be brought together by the resulting magnetic field, thereby completing a circuit through two conductors 22 and 23.

In the embodiment of the invention shown in FIG. 1, the contact elements have a resonant frequency of about 400 cycles per second and, accordingly, they will respond to all frequencies below this value but will not respond appreciably to signals of higher frequencies applied to the coil 17. One type of magnetic switch which satisfies this requirement is the switch supplied by Hamlin, Inc., designated DRR-l, for example, the coil 17 being the type S-6 coil made by the Coto-Coil Co., Inc.

In order to provide an indication of high frequency audio information, the audio signal, after passing through a 0.5 microfarad capacitor 24 which attenuates low frequencies, is applied to another magnetic switch 25 through four rectifiers 26 which may be of the 1N536 type, for example. These rectifiers are oriented so as to apply a DC. potential corresponding in amplitude to the audio signal passed by the capacitor 24 to the coil 27 of the switch 25, thereby energizing the coil in proportion to the intensities of the high frequency components so as to operate the switch contact elements 28 and 29. A power plug 30 supplies power through an on-off switch 31 and the magnetic switches 18 and 25 of the right channel to two light bulbs 32 and 33, which may be colored red and blue, for example, to represent low and high frequency information, respectively, and the corresponding signals from the left channel are similarly applied to two further light bulbs 32' and 33'. Although the invention is shown and described herein with reference to illuminating devices such as light bulbs, it will be readily apparent that any other type of electrically controlled indicating means can be utilized.

In operation, the low frequency component of an audio signal applied to the transformer 13 energizes the switch 1-8 in proportion to its amplitude, closing the switch contacts during each half cycle of oscillation so that the red light 32 is illuminated in accordance with the amplitude of the low frequency signal components and, because of its relatively low cut-off frequency, the switch 18 does not respond appreciably to high frequency signal information. After attenuation of the low frequency components by the capacitor 24, the signal is rectified and transmitted to the coil 27 so that the switch 25 responds to the amplitude of the high frequency components of the information signal, thereby energizing the blue light 33. The same operation takes place in the left channel in response to the other stereo signal applied to the transformer 13, but inasmuch as this signal differs from that applied to the right channel, the light bulbs 32 and 33 are energized differently from the lights 32 and 33 and a listener is enabled to observe the stereophonic effect visually.

If desired, the'information in each channel may be divided into three frequency components by inserting magnetic switches which have a higher cut-off frequency, e.g.,

1,000 cycles, into both channels beyond the capacitors 24 and 24 and adding further capacitors selected to attenuate frequencies below about 1,000 cycles between these magnetic switches and the switches 25 and 25'. In this case, the additional switch in each channel is connected to a third light having still another color.

In the embodiment just described, the magnetic switch coils are driven directly by the audio signals applied to the stereophonic speaker without any amplification. For systems requiring only up to about 50 milliwatts of driving power in each channel, as' measured at the loudspeaker, this arrangement is quite satisfactory. Where more driving power is necessary, however, the arrangement shown in FIG. 2may be used. According to this embodiment, the right channel input comprises a 10,000 ohm potentiometer having an audio taper and provided with a movable tap 36. From this tap, low frequency signal information is passed through a 470 ohm resistor 37 and a 0.47 microfarad capacitor 38 to the base electrode 39 of a PNP transistor 40 of the type designated 2N1380, this electrode also being joined to ground and to a negative conductor 41 through 1,000 and 33,000 ohm resistors 42 and 43, respectively. The collector electrode 44 of this transistor is connected through the coil 45 of a magnetic switch 46, which may be identical to those described previously, to the negative conductor 41, and the emitter electrode 47 is grounded. The resistors 42 and '43 provide a negative bias for the transistor to energize the coil 45 at a level just below the operating point of the magnetic switch. In addition, a 0.02 microfarad feedback operator 48 is connected between the collector and the base electrode to attenuate any high frequency components from the power source, and the coil 45 is shunted by a 1N34-type rectifier 49 to prevent reverse current surges from affecting the transistor and to permit the coil to return to the bias level rapidly after each increase in energization.

For the high frequency audio components, a'470 ohm resistor 50 and a 0.1 microfarad series capacitor 51 carry the signal from the tap 36 to the base electrode 52 of a 2N1380 transistor 53, the base electrode being biased negatively by 1,000 ohm and 33,000 ohm resistors 54 and to hold them at a level slightly below the operating level 55 in the manner previously described with respect to the transistor 40. This transistor likewise has its collector electrode 56 connected through the coil 57 of a magnetic switch 58 to the negative conductor 41 and its emitter 59 is grounded. As in the low frequency circuit, the coil 57 is shunted by a 1N34 rectifier 58a but, in this case, there is no high frequency feedback capacitor. The corresponding elements of the left channel are identical to the right channel elements thus far described and are indicated in FIG. 2 by primed reference numerals.

Power is supplied to the system of FIG. 2 from a 110 volt source through a plug 59a, an on-olf switch 60, and a fuse 61, and, to energize the negative conductors 41 and 41, a 6.3 volt-transformer 62 and a full wave rectifier v63 are provided. Also, a 100 ohm, 12 watt, resistor 65 is connected in the main power line 64 leading to the magnetic switches, and the switches 46 and 58 are connected to red and blue lights 66 and 67, respectively. In order to maintain these lights at a threshold operating level, the magnetic switches are shunted by resistors 68 and 69 respectively and, because incandescent lamps normally produce more red light thanblue light, the'res'istor 69 in circuit with the blue light has a lower resistance, such as 45,000 ohms, than the resistor 68 in circuit with the red light, which may have 55,000 ohms resistance. If desired, of course,.the magnetic switches in the FIG. 1 embodiment may be similarly shunted to' provide threshold operation .of the lights shown therein.-1Moreover, it will be readily apparent, that each channel in the system of FIG. Z-maybe divided into three or mor'e'frequency ranges rather than two.

In operation, the bias on the transistors 40, 40', 53 and 53 causes them to energize the corresponding coils of the corresponding magnetic switches. As the amplitude of a particular frequency component of the signal applied to one of the channels increases, the negativegoing portion of each cycle of oscillation drives the corresponding transistor farther on, increasing the current through the coil above the switch operating level and closing the magnetic switch to increase the intensity of the light from the corresponding light bulb. Accordingly, with stereophonic signals applied to the two channels, the two sets of lights 66 and 67, and 66' and 67 provide a visual'display of the different frequency characteristics of the signals carried by the two channels.

Although the invention has been described herein with reference to specific embodiments, many modifications and variations will readily occur to those skilled in the art. Accordingly, all such variations and modifications are included within the intended scope of the invention as defined by the following claims.

I claim:

1..An audio signal-responsive device comprising audio signal input means, a plurality of magnetic reed switch means each responsive to an audio frequency modulated magnetic field to close and open in response to changes in the instantaneous intensity of the magnetic field, a corresponding plurality of indicating means each connected to be energized through the magnetic switch means, and coil means adjacent to each magnetic switch means and connected to the input means for generating a magnetic field so as to control the switch means in response to a corresponding frequency component of an audio signal applied to the input means.

2. An audio signal-responsive device according to claim 1 wherein at least one of the magnetic switches has an upper frequency limit of operation within the audio signal range.

3. An audio signal-responsive device according to claim 1 including low frequency signal attenuating means between the input means and at least one of the coil means and including rectifier means to convert high frequency audio information to direct current potentials for application to said one coil means.

4. An audio signal-responsive device according to claim 1 including transistor means connected to energize at least one coil means in response to signals from the input means. a

5. An audio signal-responsive device according to claim -4 including bias means for biasing at least one of the coil means at a level slightly below the operating point of the corresponding magnetic switch means.

6. A stereophonic signal demonstrator comprising at least two channel means each including input means to receive separate stereophonic signals, a plurality of magnetic reed switch means each responsive to an audio frequency modulated magnetic field to close and open in response to changes in the instantaneous intensity of the magnetic field, a corresponding plurality of indicating means each connected to be energized through the mag netic switch means, and coil means adjacent to each magnetic switch means and connected to the corresponding input means for generating a magnetic field soas to control the switch means in response to the corresponding frequency component of the stereophonic signal applied to the input means.

7. A stereophonic signal demonstrator according to claim 6 wherein at least one of the magnetic switches in each channel means has an upper frequency limit of operation within the audio signal range. 8. A stereophonic signal demonstrator according to claim 6 including low frequency signal attenuating means between'the input means and at least one of the coil means in each channel means and including rectifier means to convert high frequency audio information to direct current potentials for application to said one coil means.

5 6 9. A stereophonic signal demonstrator according to References Cited by the Examiner claim 6 including transistor means connected to energize UNITED STATES PATENTS at least one coil means in each channel means in response to the audio signal from the corresponding input means. 2,148,578 2/1939 Pulhs 317 138 10. A stereophonic signal demonstrator according to 5 2,167,007 7/1939 Schott et 317 138 claim 9 including bias means for biasing at least one of the coil means at a level slightly below the operating point ROBERT ROSE Prlmary Exammer' of the magnetic switch means. WILLIAM C. COOPER, Examiner. 

1. AN AUDIO SIGNAL-RESPONSIVE DEVICE COMPRISING AUDIO SIGNAL INPUT MEANS, A PLURALITY OF MAGNETIC REED SWITCH MEANS EACH RESPONSIVE TO AN AUDIO FREQUENCY MODULATED MAGNETIC FIELD TO CLOSE AND OPEN IN RESPONSE TO CHANGES IN THE INSTANTANEOUS INTENSITY OF THE MAGNETIC FIELD, A CORRESPONDING PLURALITY OF INDICATING MEANS EACH CONNECTED TO BE ENERGIZED THROUGH THE MAGNETIC SWITCH MEANS, AND COIL MEANS ADJACENT TO EACH MAGNETIC SWITCH MEANS AND CONNECTED TO THE INPUT MEANS FOR GENERATING A MAGNETIC 